The operator requires a 12¼" tangent borehole through interbedded shale, chalk/sandstone that contains hydratable montmorillonite clay, Auk North field, UK North Sea. The swelling clay and long open-hole section have proven troublesome creating hole cleaning issues, frequent wiper trips and stuck pipe events. A comprehensive modeling project was initiated with the aim of reducing vibration whilst improving rate of penetration (ROP) by selecting the best drive system, bottom hole assembly (BHA) configuration and combination of operating parameters. A rock strength program was run and indicated unconfined compressive strength (UCS) of the Oligocene/Eocene formations at 2-10kpsi. Analogous formation samples were selected from the rock library and laboratory tests were conducted to replicate actual drilling conditions. The resulting data was then entered into the finite element analysis (FEA) based modeling system. A 12¼" × 14" concentric reamer equipped with three polycrystalline diamond compact (PDC) triple row cutter blocks, a pilot PDC bit and a rotary steerable system (RSS) were selected for the investigation. Dynamic simulations were preformed with various operating parameters to observe how changes influenced BHA performance. The analysis provided valuable insight when the bit and reamer are drilling non-homogeneous formations. The weight-on- tool fluctuation creates BHA instability which can be mitigated by managing parameters. A driller's roadmap was produced showing optimum weight on bit (WOB)/revolutions per minute (RPM) combinations that would produce stable drilling for different formation scenarios. The integrated BHA was run with the recommended parameters and drilled 5889ft in three runs at an average ROP of 77ft/hr. The BHA met all directional objectives with low lateral vibration and medium stick-slip levels. All cutting structures used showed minimal wear. The successful run enabled the operator to complete the section seven days ahead of authority for expenditure (AFE) plan.

Modern Mobile Offshore Drilling Units (MODU) are equipped to ensure they are able to cope with the demands of both current and future offshore well design challenges which may be located in either in deep water or inmature basins like the North Sea thatrequire significant measured depths to reach the intended target. With all of this drilling power, such as topdrives capable of producing over 75,000ft-lbs of continuous torque and multiple mud pumps each with the ability to flow in excess of 1,000gpm it is readily possible to damange the wellbore by over using the available capacity of the rig. In reality this surfeit of available energy, if not used judiciously, can potentially result in unexpected problems. Much has been written in the past with regards to ensuring that the available rig capability is best utilised to achieve complex well objectives and a great deal of the techniques developed in extended reach and complex well drilling operations were designed to make the most of the capacity available. Now, with high specification rigs these techniques identified originally in the early to mid-1990's, though still valid need to be used with care and consideration since the rig capabilities have advanced significantly such that without a degree of caution it is possible to cause significant damage to the downhole tools or wellbore and potentially loose either the section or the well altogether. Whilst many of the techniques often termed ‘good oilfield practice’ are still valid there are now additional considerations which have to be incorporated into both the well plan and the day-to-day operations on the rig to ensure that best use can be made of the rig's capability. This paper aims to show how one operator successfully used a modern, high-specification jack-up rig to access a remote reservoir where challenging drilling conditions presented a number of potential obstacles to achieving the well objectives.